Since numerous users may be parked in a parking lot simultaneously, it may be difficult for a particular driver to find their vehicle upon exiting a store. In some cases, a car horn or alarm may be used, but since many horns and alarms sound similar, it can be difficult to distinguish between various vehicles.
Some attempts to change this experience include U.S. Ser. No. 09/653,388, which generally relates to a lost item finding system including at least two nearly identical locators. Either one can be used to find the other and whatever items are attached to it. The available locator broadcast to the lost one an acoustic search signal including a sequence of tones having predetermined frequency differences between them. The lost locator determines the baseline frequency and then identifies whether the signal conforms to the predetermined tone sequence and then transmits a beacon signal that can be perceived by the user as he searches for the lost item. The beacon signal may include both an audible signal and a flashing light emitting diode. Advantageously, both the transmission and reception of the audio signal is accomplished with one piezoelectric transducer, and the efficiency of the transducer is increased by forming a resonant cavity having a cap both protecting the piezoelectric transducer and forming an annular side port.